IDH mutations are the most common genomic aberration, occurring in nearly 80% of lower grade gliomas.6 IDH mutations are not unique to gliomas, however, as they may also be found in many other cancers, such as cholangiocarcinoma, acute myeloid leukemia, melanoma, and uterine corpus endometrial carcinoma.7 IDH mutation is thought to be an early driving event in the development of astrocytomas and oligodendrogliomas. The gene discussed is IDH1; the disease is cholangiocarcinoma.